Previously Unknown Species Sheds Light on Mechanism of Radiotolerance in Tardigrades

Using genome, transcriptome, and proteome analysis of the newly-discovered species of tardigrade, named Hypsibius henanensis, scientists explored the molecular basis contributing to radiotolerance in these tiny invertebrates.

Tardigrades, also known as water bears or moss piglets, are a diverse group of microscopic invertebrates famous for their ability to withstand extreme conditions.

First discovered in 1773, these creatures can live for up to 60 years, and grow to a maximum size of 0.5 mm, best seen under a microscope.

They are able to survive for up to 30 years without food or water, for a few minutes at temperatures as low as minus 272 degrees Celsius (minus 457 degrees Fahrenheit) or as high as 150 degrees Celsius (302 degrees Fahrenheit), and minus 20 degrees Celsius (minus 4 degrees Fahrenheit) for decades.

They withstand pressures from virtually 0 atm in space up to 1,200 atm at the bottom of the Marianas Trench.

They also exhibit exceptional resistance to ionizing radiation, withstanding doses as high as 3,000 to 5,000 grays (Gy) of gamma rays, which is approximately 1,000 times the lethal dose for humans.

The mechanism of radiotolerance in tardigrades remains largely unclear.

Previous studies investigating how they do this have shown that tardigrades possess robust DNA repair capabilities.

They also express a tardigrade-specific protein called damage suppressor (Dsup), which, when expressed in human cells, protects DNA from radiation damage.

In new research, Qingdao University Lei Li and colleagues described a new species of tardigrade: Hypsibius henanensis.

Through detailed morphological and molecular analysis, they also explored the basis of the species’ radiotolerance.

The researchers evaluated how exposure to heavy ion radiation altered the animal’s molecular profiles. They found that 285 stress-related genes were upregulated.

They further uncovered three molecular mechanisms that contribute to radiotolerance in the organisms.

First, the horizontally transferred bacterial gene DOPA dioxygenase 1 (DODA1) enhanced radiation resistance by producing betalains — pigments with potent free radical scavenging properties typically found in plants, fungi, and bacteria.

Second, a tardigrade-specific protein, TDP1, facilitates the repair of DNA double-strand breaks.

Lastly, the mitochondrial chaperone gene BCS1, which expanded during tardigrade evolution, is uniquely upregulated in response to radiation, shielding cells from radiation-induced mitochondrial damage.

“Extreme environmental resistance of extremophiles such as tardigrades is a treasure trove of unexplored molecular mechanisms of stress resistance,” the authors said.

“Functional research on these radiotolerance mechanisms will further broaden our understanding of cellular survival under extreme conditions and may provide inspiration for promoting human health and combating disease.”

The results were published October 25, 2024 in the journal Science.

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Lei Li et al. 2024. Multi-omics landscape and molecular basis of radiation tolerance in a tardigrade. Science 386 (6720); doi: 10.1126/science.adl0799